## baldymcgee6 3 years ago Partial Derivatives... posted below

1. baldymcgee6

|dw:1351748975295:dw|

2. hartnn

partial derivative means u treat other variable as constant. u know this ?

3. baldymcgee6

Right, so we treat y as a constant in the first one..

4. Dido525

Which variable are you taking constant>?

5. hartnn

yes.

6. baldymcgee6

|dw:1351749134665:dw|

7. hartnn

absolutely! that was my next statement, that u need log diff. here.

8. baldymcgee6

In my experiences with log diff I always had a function in the form of y = f(x)^g(x).... So what do we do here?

9. baldymcgee6

do we write y = ......?

10. hartnn

taking log on both sides, u get log y = g(x) log f(x) then use product rule

11. hartnn

u'll also need a chain rule for this....

12. baldymcgee6

|dw:1351749340629:dw|

13. hartnn

oh dear! the y on left and on right are different, u should have used g or some other letter

14. baldymcgee6

oohhhhhh.. that's where I went wrong... this is off my last quiz :/

15. baldymcgee6

so it'll be g'/g on the left?

16. hartnn

yes, after doing product rule , u resubstitute for g

17. baldymcgee6

|dw:1351749800366:dw|

18. hartnn

thats right

19. baldymcgee6

|dw:1351749846652:dw|

20. hartnn

absolutely correct

21. hartnn

same for 2nd question, just replace x with y and y with x

22. baldymcgee6

right... I just messed up on calling the function y... messed with my head.

23. baldymcgee6

thanks again for the insight!

24. baldymcgee6

I'm not going to do the second derivative, I think I can get it... Thanks so much!

25. baldymcgee6

I mean, i'm not going to do it on here.. :)

26. hartnn

ok, welcome ^_^